A pneumatic tire generally comprises a carcass (or “casing”), a tread, sidewalls and bead regions. The tread belt is generally cylindrical, having an inner diameter, an outer diameter, a height, and an overall thickness. A number of belt components, also generally cylindrical, may be incorporated into the tread package. For passenger car and light truck tires, all these components are molded into a single tire. “Green” uncured tire components are laid up on a build drum which is expanded to form the casing, then the casing is put into a mold where the tread is applied and the tread pattern is molded into the external surface of the tread package.
Earthmoving tires are very expensive, and since the tread typically wears out before the casing (or “carcass”) wears out, a separate “tread belt” component is designed to be removable and replaceable. This forms what is known as a “two piece” tire. Often in a two piece tire, the inner surface of the tread belt is molded to have circumferentially-extending grooves which are spaced apart and parallel with one another and which mate with circumferentially-extending ridges on the outer surface of the tire carcass. The grooves and ridges may be appropriately tapered to facilitate the ridges inserting firmly into the grooves. Generally, the expansion of the tire carcass when it is inflated holds the tread belt in place, and the mating grooves and ridges help prevent the tread belt from moving axially with respect to the tire carcass. The large surface area of contact between the tread belt and the coefficient of friction, prevents the tread belt from spinning circumferentially upon the carcass.
Two piece, tread belt pneumatic tires are currently typically very large tires (greater than 119.9 inches outside diameter (OD)) generally designed for use on very large vehicles, generally off-the-road vehicles such as earthmovers and large capacity mining trucks (e.g., 300 short tons or more). The size of these tires is extremely large. For an example, the tire weight can be approximately 8,000 pounds (3,628 kg) to 15,000 pounds (6,803 kg) or more for an unmounted tire. When using a two-piece type tire wherein the tread belt forms the outer structure and the inner structure is formed by a carcass wherein the two parts are separable, the tread belt alone will weigh over 4,000 pounds typically, many times more depending on the size. By way of example, a 57 inch nominal rim diameter two-piece tire having a 45R57 size will have a tread belt assembly having an outside diameter of approximately 12 foot or roughly 144 inches and will weigh approximately a little more than 4,500 pounds. Likewise, a smaller but still very large 51 inch nominal rim diameter tire of a 3300R51 size can yield a 3000 lb. tread belt.
FIG. 1 illustrates a generic two piece pneumatic tire 100 having a carcass comprising two sidewalls and a crown extending between radially outer ends of the sidewalls. Beads are disposed in a bead region at the radially inner ends of the sidewalls. A tread belt is disposed around the crown. The tire has a centerline CL which will be coincident with its axis of rotation. The tire has an equatorial plane EP and is generally symmetrical about the EP. The tire has an inner diameter (d1) which is essentially the diameter of a rim (not shown) to which the tire will be mounted. The tire has an outer diameter (d2) which is the outer diameter of the tread belt when properly mounted on the tire carcass. The tire has a width (W1), from sidewall-to-sidewall (or, across the tread belt). At the left hand side of FIG. 1, the tread belt is shown spaced apart from the crown (exploded view) for illustrative clarity. Here can be seen the ridges and grooves on the inner surface of the tire belt, and the corresponding (mating) grooves and ridges on the outer surface of the crown portion of the tire. This is all well known.
Presently, tread belts are laid up and cured in individual cure stations. These stations are costly to build, maintain, and operate. These stations can also produce only one specific type of product and generate only a quantity of one product at a time. In the molding concept that will be hereunto declared, the functionality of which, in combination with the conventional means of a pot-heater, replaces that of these costly cure stations. The current process calls for great energy utilization within the cure station to procure the belts in addition to great energy utilization in the pot heater to procure the casings. Utilization of the pot heater allows for greater flexibility of product cure variation and reduces the amount of energy needed to cure both products needed to produce the two-piece tire.